Golang Image.At方法代碼示例

// blendCheckered is basically a copy of xgraphics.Blend with no interfaces.
// (It's faster.) Also, it is hardcoded to blend into a checkered background.
func blendCheckered(dest *xgraphics.Image) {
	dsrc := dest.Bounds()
	dmnx, dmxx, dmny, dmxy := dsrc.Min.X, dsrc.Max.X, dsrc.Min.Y, dsrc.Max.Y

	clr1 := xgraphics.BGRA{B: 0xff, G: 0xff, R: 0xff, A: 0xff}
	clr2 := xgraphics.BGRA{B: 0xde, G: 0xdc, R: 0xdf, A: 0xff}

	var dx, dy int
	var bgra, clr xgraphics.BGRA
	for dx = dmnx; dx < dmxx; dx++ {
		for dy = dmny; dy < dmxy; dy++ {
			if dx%30 >= 15 {
				if dy%30 >= 15 {
					clr = clr1
				} else {
					clr = clr2
				}
			} else {
				if dy%30 >= 15 {
					clr = clr2
				} else {
					clr = clr1
				}
			}

			bgra = dest.At(dx, dy).(xgraphics.BGRA)
			dest.SetBGRA(dx, dy, xgraphics.BlendBGRA(clr, bgra))
		}
	}
}

// drawPencil takes an (x, y) position (from a MotionNotify event) and draws
// a rectangle of size pencilTip on to canvas.
func drawPencil(canvas *xgraphics.Image, win *xwindow.Window, x, y int) {
	// Create a subimage at (x, y) with pencilTip width and height from canvas.
	// Creating subimages is very cheap---no pixels are copied.
	// Moreover, when subimages are drawn to the screen, only the pixels in
	// the sub-image are sent to X.
	tipRect := midRect(x, y, pencilTip, pencilTip, width, height)

	// If the rectangle contains no pixels, don't draw anything.
	if tipRect.Empty() {
		return
	}

	// Output a little message.
	log.Printf("Drawing pencil point at (%d, %d)", x, y)

	// Create the subimage of the canvas to draw to.
	tip := canvas.SubImage(tipRect)

	// Now color each pixel in tip with the pencil color.
	tip.For(func(x, y int) xgraphics.BGRA {
		return xgraphics.BlendBGRA(canvas.At(x, y).(xgraphics.BGRA), pencil)
	})

	// Now draw the changes to the pixmap.
	tip.XDraw()

	// And paint them to the window.
	tip.XPaint(win.Id)
}